Gate valves are generally comprised of a valve body having a central axis aligned with inlet and outlet passages, and a space between the inlet and outlet passages in which a slide, or gate, may be moved perpendicular to the central axis to open and close the valve. In the closed position, the gate surfaces typically seal against sealing rings which surround the fluid passage through the valve body. In the petroleum industry, gate valves are used along piping at various locations, and in particular are used in piping referred to in the petroleum industry as a Christmas tree, which is used as part of a drilling operation.
Gate valves may be operated manually or automatically. One method to automatically operate a gate valve is to use an actuator. An actuator is a mechanical device for moving or controlling a mechanism or system. When an actuator is used in a gate valve, the actuator is typically linked to a stem to repeatedly move the valve gate between open and closed positions.
Actuators to open and close the gate valves may include manual operators, diaphragm-type operators, and hydraulic operators. The actuator may include a bonnet assembly, which interconnects the valve body and the valve gate, and a bonnet stem which is movable with the gate via an operator.
A manual operator is often seen combined with diaphragm or hydraulic operator for back up purposes. These combinations generally result in a top shaft extending from the operator. The extension of the top shaft may indicate whether the valve is open or closed.
When using a manual operator with a diaphragm-type or hydraulic having a top shaft extending from the operator, care must be undertaken to ensure that torque is not applied to the top shaft. Torque applied to the top shaft may cause gate, gate seal, or drift misalignment. Additionally, excess torque of the top shaft may cause shearing of the top shaft or other damage to the internal components of the actuator.
It therefore may be desirable to have an actuator with a top stem having qualities of increased torque resistance.